Integrated circuit chips are conventionally enclosed in a package that provides protection from environmental conditions and enables electrical interconnection between the chip and another electrical component, such as a printed circuit board or a motherboard. A semiconductor package includes a supporting leadframe having leads, a chip electrically coupled to the leadframe, and encapsulating material molded over a surface of the leadframe and the chip. The encapsulating material defines an exterior surface of the package through which the leads are exposed for subsequent electrical connection to printed circuit boards and the like.
The leadframe provides a support structure for the package. When the package is singulated, or severed from its carrier, the leads of the leadframe are exposed. Copper or copper-based leads are known to oxidize in the presence of air. Oxidized leads have reduced or unacceptable electrical properties. Some copper leads are plated by a galvanic process with tin to minimize oxidation of the leads. However, tin is susceptible to the formation of whiskers, or needle-like tendrils, that have the potential to undesirably cause electrical shorts in the finished package. Some copper leads are plated by a galvanic process with an alloy of tin and lead (Pb) to minimize oxidation of the leads. Alloys of lead (Pb) are environmentally undesirable.
For these and other reasons there is a need for the present invention.